Photographic process with exposure diminution



'@v, 9, 1937. L.. 'I'.TRQLND $998,442,

PHOTOGRAPHIIC PROCESS WITH EXPOSURE DIMINUTION Original Filed Aug. l0,1953 auf /Pfca Patented Nov. 9, 1937 PHo'roGnAPHro PnooEss WITH Expo-SURE DnvnNU'rroN Leonard T. Troland, deceased, late of Cambridge, Mass.,by Cambridge Trust Company, executor, Cambridge, Mass., assignor toTechnicolor Motion Picture Corporation, Hollywood, Calif., a corporationof Maine Original application August 10, 1933, Serial No.

684,546. Divided and this application November 16, 1935, Serial No.50,161

s claims. (ci. :a5-2i This application is a division of prior applil Itis well known that latent photographic records produced with light of acertain wave length range, if subsequently exposed to rays of a higherwave length, are photographically diminished or retrogressivelydestroyed in proportion to the intensity of the second exposure Thisphenomenon is commonly referred to as Herschel effect and is perhapsrelated to the well known solarization phenomenon which consists insubstance in the fact that a prolonged or otherwise very intensiveexposure may, after development, result in a blackening of thephotographic emulsion to a lower degree than the blackening effected byweaker light intensities. However, whereas solarization depends uponprolonged exposures, the Herschel effect appears to be substantiallyindependent therefrom and Amerely 'dependent upon the cooperation ofconsecutive exposures with light of different wavelengths. Althoughscientists do not quite agree upon the exact nature or theory of theHerschel effect, it is an established fact that the effect of an initialor primary exposure upon a photographic emulsion is reversed uponexposure to light waves of higher wave length, herein referred to assecondary. exposure, and that this result is more rapid, certain andproportional to the intensity of the secondary exposure than any effectthat'might be obtained with ordinary solarization.-

It has been found that this so-called Herschel eeot lends itself verywell to practical application and permits the carrying out of certainphotographic operations which could otherwise not be undertaken at allor only with difficulty. These practical applications make use of theiact that the Herschel effect permits the quantitative subtraction ofexposures, which subtraction permits the introduction of a newphotographic method of the general nature of an inversion of heretoforeknown photographic procedures, which method in its variouspossibilities, is of `considerable practical value.

Although it is herein referred to, the Herschel eiect, it is understoodthat the prescrit invention is not limited to the utilization of thisphenomenon as defined at any given stage of development of thephotochemical science, (which denitions might very well vary to aconsiderable extent), but that it embraces, independently of anyvproposed theory or explanation, the herein described practicalapplications of the possibility of diminishing or reducing the intensityof a photographic record by means of a secondary exposure, as defined inthe appended claims.

cation Serial No. 684,546, filed August 10, 1933.

The new method will be explained in its generic v aspect as well as in aspecic example, with reference to drawing, in which:

Fig. l. is a set of density-exposure curves indieating the eiect ofprimary and secondary exposures employed in the present method; and

Fig. 2 is allow diagram illustrating the invention as applied to theseparation of color records.

In its generic aspect, the invention proposes the combination ofpictorial photographic records by means of primary and secondaryexposures, whose effect will rst be generally explained. In Fig. l,

, A is the well-known Hurter and Driilield curve,

commonly referred to as H and D curve, of a given emulsion, whichpresents densities of a developed record plotted over the logarithms ofeiiective exposures, that is, over the log (iXt) where z' is theexposure light intensity and t the exposure time, the product beingmeasured in candle meter seconds. Bis a similar curve, signifying theHerschel eect, obtained by varying secondary exposures of a plate,uniformly pre-y exposed to light of a certain Wave lengtli,'to light ofa higher wave length. Point b of curve B corresponds to the densityobtained with asecondary exposure Zero, that is, to the density of thedeveloped pre-exposed plate not subjected to any secondary exposure. Theother points of the drooping curve correspond to developed densitiesobtained upon increasing amounts of secondary exposure, and it isevident that the ratio of density decrease is fairly uniform over thedensity range corresponding tothe substantially straight partA of curveA. Curves C, D similarly signify theeect of secondary exposuressubsequent to primary exposures which, without secondary exposures,would result in lower densities, c, d, as indicated.

It is therefore apparent that, if a photographic emulsion is exposed toan object iield, certain portions receiving equalprimary exposures whichwould result in density b, and if three of these portions arethensubjected to diierent secondary exposures h1, h2, h3, for example,through a photographic record, and developed, the densities of theseportions will be reduced to d1, d2, d3, respectively, as indicated inFig. 1.

On the other hand, if pointscf direrent primary exposures, that is,points which would have densities b, c, d, if developed without previoussecondary exposure, are subjected to a certain unithan a superpositionof densities.

suitable portions of primary and secondary exposure curves can beselected, and since the shapes of these curves can be controlled withreasonable certainty, it is evident that not only can two exposures besubtracted without disturbing the density gradients of the exposures,especially by using the substantially straight line portions of theexposures, but also that the density gradients vof exposures can bechanged at will, as will be explained morein detail hereinafter. l

It should be observed that we are herein dealing not with thesubtraction of densities, that is, speaking in terms of the H and Dcurve, the subtraction takes no place between the ordinates of thecurves, but that the Herschel effect involves Y rather an arithmeticsubtraction of exposures inside the expression (log E) for the abscissasof the curve, as for example, log (e-h) if e signies a primary and h asecondary exposure. It must thereby be observed, however, that it is notgenerally possible with elementary means directly to relate e and h, dueto the different nature of the two exposures, so that the above way ofexplaining the operation of the Herschel eiect with sets of curves forthe primary and secondary exposures is perhaps the preferable expedientfor -it is possible to separate superposed records of diiferent coloraspects of an object field, which records are contained in the emulsionof a socalled monopack film. By rst copying the records insuperposition, then removing one record, and printing the remainingrecord and the first copy together, it is possible to obtain a separateduplicate of the removed record. However, such methods can only beemployed when the records are substantially independent and involve asuperposition of separately produced densities in essentially distinctemulsion layers. 'I'hese methods are not applicable where a compositerecord involves an addition'of interpenetrative exposures in a singleemulsion stratum rather When such conditions prevail, the Herscheleffect provides -means for the subtraction of a given color record-'from a composite record of this interpenetrative exposure type, sinceit permits to subtract exposures rather than densities. A good exampleof emulsionsbearing interpenetrative exposures i is the front emulsionof a bipack which records the i red color aspect in front of a mainlyblue sensitive emulsion, for the purpose of obtaining a sharp red recordand transferring the diffusion blur to the blue record whereit is ofminor disadvantage. Bipacks of this kind are well known in the art andfor example described in British Patent No. 321,998, for Improvements inor relating to three-colour photography, to Thomas Thorne Baker. Bipacksof this type have the outstanding disadvantage that the red recording,and

V--therefore red sensitive 'front emulsion, is necessarily moreor lessblue sensitive, so that the red record is always adulterated with a bluerecord, this adulteration involving, due to its nature, a

summation of interpenetrating exposures rather than a superposition ofdensities. 'Ihis blue. adulterating exposure is, for obvious reasons,very undesirable, but can be eliminated from the red sensitive front nlmby utilizing the Herschel effect according to the present invention, forexample in the following manner:

, The bipack front illm containing the composite red and blue exposureis developed, and a latent composite positive printed therefrom, thisprinting step constituting a primary exposure in the sense of this termas herein used. This latent record is then exposed, through theconventionally tially pure and unadulterated red record posi-A tive,from which a pure red record duplicate negative can be made, which, withthe black illm record, constitutes a. complementary pair ofunadulterated color aspect records. It is of course understood thatinstead of secondarily exposing a latent positive to a. substantiallypermanent negative, a' latent composite negative, for example, theoriginal negative, can be exposed to a positive, for example, theoriginal back film record.

The emulsions used for practically utilizing the Herschel eifect must beselected with a view to suitability for that purpose. Good results wereobtained with customary emulsions, preferably treated prior to use bybathing in a 1 to 2% solution of potassium bromide for about ve minutes,with Subsequent drying. It was also found that dyed emulsions suitablefor making gelatine matrices, of the type as described in the sameinvention eopending application Serial No. 454,973, led May 23, 1930,matured into Patent No. 2,044,- 864 of June 23, 1936, are especiallysuitable for purposes of the prent invention. The primary exposure maybe made with daylight, or with the customary artificial light sourcesused for photographic negative and positive processes, whereas secondaryexposure with light of a wave length of approximately 700 to 780;'. wasfound to be satisfactory, although experiments with primary X-rayexposures and secondary exposures with white light also gives acceptableresults. 'The primary exposures do not substantially differ fromordinary exposures, whereas, concerning duration, it is dlilicult togive exact data for the secondary exposures, since they depend a gooddeal upon the conditions in each particular case. It was found that anemulsion having received a primary exposure corresponding to a customaryprinting exposure of about one-half second, gave, in the abovedescribedmonopack process, satisfactory results witha secondary exposure throughthe blue record with light concentrated from a high-power tungstenillament lamp filtered through a illter passing substantially the abovevgiven spectral range, for

about five totwenty seconds, depending on the strength of the lightsource, and the record density. A suitable filter is any of thecommercial infra red filters., or a combination of a so-called DarkTheatre Blue" filter and a Selenium Red (Nos. 503 and 242, listed in;the publication entitled Glass Color Filters ofthe Corning Glass Works)glass filter, which transmits practically only infrared light, with avery small percentage of visible deep red.

'I'hls improved bipack (or tripack) method is schematically illustratedin Fig. 2, where W is a bipack with a front lm comprising support S'with red-blue sensitive emulsion E' and a back iilm comprising supportS" withblue sensitive emulsion E. Emulsion E contains a red record R'adulterated with a record substantially corresponding to the blue-recordB of emulsion E". The two bipack component iilms are nished as usual anda master positive fihn G with emulsion H and support T is then exposedto record R' with light L so that emulsion H receives a latent record Kwhich is a positive of record R and comprises the adulteration of thelatter. Subsequently, Without intermediate treatment, emulsion H issubjected to a secondary exposure with high wave length light L' throughnegative record B. This secondary exposure reduces the latent record Kaccording to a pattern which corresponds to the blue record B', so thatthe new latent record K does not contain the adulterating blue componentwhich was present in latent record K. Care must of coursebe taken thatthe secondary exposure of G is so adjusted that not more exposure issubtracted from record H than corresponds to the blue adulteration' ofrecord R'. After development, lm G represents a correct positive K ofthe red color aspect, which, together with the initially correct bluenegative record B' can be further utilized according to conventionalmethods.

Concerning the illustration of the` invention in Fig. 2, it should beremarked that the record patterns are indicated by varying thicknessonly (as it would be present, at least substantially, in emulsionshaving incorporated highly light absorbing substances) whereas thesepatterns might as Well be represented by varying overall particledistribution.

It has been found that primary exposures with X-rays as mentionedbefore, and secondary exposures with radiations of higher wave length,which in' this case may be ordinary white light, can be employedadvantageously, especially in instances where 'a uniform primaryexposure is applied. It has also been found that treatment in certainsubstances of the class known in the art as desensitizers (as forexample phenosafranine) intermediate primary and secondary exposure,inlluences the latent record of the emulsion so as to permit the use oflight of substantially the same wave lengths for both primary andsecondary exposure. It will be apparent that these phenomena,

as far as their practical application to pictorialy photography isconcerned, are in their action quite similar to that of the Herscheleiect which is herein morev particularly described, and that one or theother will be preferably used according to convenience and expediency.

It should be understood that the present disclosure is for the purposeof illustration only, and that this invention includes all modicationsand equivalents which fall within the scope of the appended claims.

. What yis claimed is:

l. The method of combining photographic records, which comprises makingin an emulsion layer of the silver halide type a latent record of anobject eld and in register therewith in a second emulsion layer asubstantially permanent record of another aspect of the same leld, saidrst layer receiving a record component substantially in conformity withsaid second record,

and exposing said latent record in register through said permanentrecord with light photographically diminishing said latent record inamounts controlled by the permanent record, thereby diminishing saidcomponent in said rst layer.

2. The method of producing photographic records of different coloraspects of an object field,

which comprises making in an emulsion layer of the silver halide type alatent positive record of a certain color range and in 'a secondemulsion layer a negative record of the same object iield, but of asmaller color range substantially included in the range of said latentrecord, said rst layer receiving a record component substantially inconformity with said second record and exposing said latent recordthrough said negative record with light adapted photographically todiminish said latent record, whereby said negative'record issubstantially subtracted from said latent record, thereby diminishingthe color range recorded in said first layer.

3. The method of producing photographic records of different coloraspects of an object eld, which comprises making in'an emulsion layer ofthe silver halide type a latent negative record of a certain color rangeand in a second emulsion layer a positive record of the same object eld,but of a smaller color range substantially included in the range of saidlatent record, said first layer receiving a recordcomponentsubstantially in conformity with said second record and exposing saidlatent record through said positive record with light adaptedphotographically to diminish said late nt record, whereby said positiverecord is substantially subtracted from said latent record, therebydiminishing the color range recorded in said rst layer.

4. The method of producing photographic records of different coloraspects of an object eld,

which comprises making in an emulsion layer a record of a certain colorrange of said object field, making in a second emulsion layer a secondrecord of the same object iield with a second color range that isincluded in said rst color range, said first layer receiving a recordcomponent substantially in conformity with said second record, copyingsaid rst recordon a photographic silver halide emulsion, and exposingsaid emulsion to said second record in register with thelatentrecordcontained therein, with light of a lower wave length than that of thecopying exposure thereby .diminishing the color range in said rstrecord.

5. The. methodI of combining vphotographic records, which comprisessuperposing two emulsion layers one of which is sensitive to a greaterspectral range than the second layer, exposing said layers whereby saidrst layer receives an exposure component substantially coniorming to theexposure of said second layer, making a developed record correspondingto the exposure in said second layer, providing a latent silver halidegelatine record of the exposure in said lirst layer, said developedrecord and said exposure component in said latent record beingapproximate photographic complementals, and exposing said latent recordthrough said developed record with light photographically diminishingsaid latent record, thereby diminishing said exposure component in saidiirst layer.

6. In the art of color photography the method which comprisessuperposing an emulsion layer Ainsensitive to red light and an emulsionlayer tsensitive to red and to the sensitivity range ofl second layerreceives an exposure component substantially conforming to the exposurein said rst layer, making a developed record corresponding to theexposure in said rst layer, providing a latent silver halide gelatinerecord of the exposure in said second layer, said developed record andsaid exposure component in said latent record being approximatephotographic complementals, and exposing said latent record throughsaiddeveloped record with light photographically diminishing said latentrecord, thereby diminishing said component in said second layer.

^ CAMBRIDGE TRUST COMPANY, Executor of the Last Will and Testament ofLeonard T. Troland, Deceased.

By A. MEAD WHEELER, Assistant Secretary.

